Type B coxsackieviruses (CVB) are the most common infectious cause of myocarditis, a serious disease that can lead to dilated cardiomyopathy and cardiac failure. The host responses that control CVB are not well defined, and I have used a murine model of CVB3 infection to investigate this issue. I have found that CVB3 induces minimal CD4 or CD8 T cell responses in lymphoid and peripheral tissues, and this may be associated with impaired dendritic cell (DC) activation and/or antigen (Ag) presentation. Several picornaviruses, including CVB3, can modulate the expression of major histocompatibility complexes (MHC) and/or costimulatory molecules on virus-infected cells. I hypothesize that DC infection by CVB3 inhibits the up-regulation of MHC and/or costimulatory molecules. Moreover, I suggest that CVB3 infection severely diminishes MHC Class I viral Ag presentation. Innate recognition of viral materials can trigger DC maturation, and I propose that uptake of CVB3-infected cells induces up-regulation of MHC Class II, but not Class I, which curtails viral Ag-presentation to CD8 T cells. The specific aims are: (1) to characterize DC activation during CVB3 infection in vivo, and determine if direct infection of DCs by CVB3 impedes their activation and functions;and (2) to evaluate how innate recognition of CVB3 by DCs affects cell activation and presentation of virus-encoded Ags, and to identify the innate virus sensor required for recognition. First, I will use multi-parameter flow cytometry to determine which DC subsets are activated and recruited by CVB3 infection in vivo. Second, I will use a recombinant CVB3 expressing green fluorescent protein to identify virus-infected DCs in vivo and analyze the expression of MHC and costimulatory molecules. Third, I will test whether CVB3-exposed DCs can produce antiviral cytokines and present MHC Class I and ll-restricted viral antigens to epitope-specific T cells;this will be evaluated with virus-infected DCs, or with DCs that have taken up CVB3-infected cells, using bone marrow- derived DC cultures in combination with ELISA and intracellular cytokine staining. Fourth, I will define the innate viral sensor(s) important for CVB3 recognition and DC activation by examining how loss of gene expression impacts innate response protein up-regulation, using gene knockout DCs and western blot. PUBLIC HEALTH RELEVANCE: Coxsackievirus B (CVB) infection is the most common infectious cause of heart inflammation and can lead to chronic disease and cardiac failure. This research will enrich our understanding of how CVB modulates the immune response, and may contribute to the development of novel methods to more effectively treat virus infection, thereby reducing the incidence of virus-induced cardiovascular disease.